I needed to create a religion for my Endland campaign and boy, that's not easy. It couldn't be too radical because the priest lives in a town where intolerance is very much frowned upon. It gets in the way of commerce. So the cults suggested in the rulebook were out.
After some hanging around at Wikipedia, I came across this very cool religion chart where you can find a short summary of origin, pratices and believes of a great many religions. That came in handy, but what really gave me good ideas was the random religion generator at Chaotic Shiny. I used the checklist I found there to come up with something on my own, but if you need a religion in a hurry, this is brilliant.
There are other random generators there, from names, animals, weather, conspiracies to whole medieval cities. The setting mashup generator is hilarious. Renaissance China and zombies or Modern Belgium and monkies. Yeah, I can totally see that.